Our boys love those building brick storage bins that you can get at big box retailers. We, however, do not love the price. Here's our version that cost less than $5 each and the kids can switch up the faces.
Spray paint the bucket(s) and let it dry.
We did a quick internet search to find easy to trace monster faces to print out. Lay the template on top of the non-paper side of contact paper and tape it down. Use a small utility knife to cut out the various pieces. Use a permanent marker to add in some details.
Glue a large building block onto the center of the lid.
Remove the backing from the contact paper and add to the bucket.
Dump all the kids' building blocks into the bucket.
When they get bored with the faces, they can easily swap them out with others.